[petsc-users] one compilation error in PETSc-dev with enabling GPU and complex number

[Jack Poulson]

Thank you for the relevant links!

The downside is that there does not seem to be a proposal to allow for more
general base types within std::complex, e.g., __float128. This is actually
my major complaint (that and fear of unstable complex arithmetic,
especially division).

Jack

On Tue, Feb 7, 2012 at 1:19 PM, Chetan Jhurani <chetan.jhurani at gmail.com>wrote:

> I’ve faced similar issues with std::complex, but the material below,****
>
> which is not in the C++ standard, has suppressed my fears.  Not****
>
> eliminated though.****
>
> ** **
>
> http://fftw.org/doc/Complex-numbers.html (has a broken link, corrected
> below)****
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1388.pdf****
>
> ** **
>
> Chetan****
>
> ** **
>
> *From:* petsc-users-bounces at mcs.anl.gov [mailto:
> petsc-users-bounces at mcs.anl.gov] *On Behalf Of *Jack Poulson
> *Sent:* Tuesday, February 07, 2012 10:10 AM
> *To:* PETSc users list
> *Subject:* Re: [petsc-users] one compilation error in PETSc-dev with
> enabling GPU and complex number****
>
> ** **
>
> On Tue, Feb 7, 2012 at 11:29 AM, Matthew Knepley <knepley at gmail.com>
> wrote:****
>
> On Tue, Feb 7, 2012 at 11:20 AM, recrusader <recrusader at gmail.com> wrote:*
> ***
>
> Whether is it possible to find an efficient mechanism to do the conversion
> between std::complex and cusp::complex when the conversion is necessary.**
> **
>
> ** **
>
> That does not matter. This is a compile error. We are not going to change
> this right now, and it seems like you are not going****
>
> make the necessary changes, so I would say that complex numbers are not
> supported with our GPU code right now. The****
>
> change would involve using cusp::complex for PetscScalar, and I am not
> sure how much work that would entail.****
>
> ** **
>
>    Matt****
>
>
> Matt, ****
>
>
> You might be interested to hear that the C++03 standard states that "The
> effect of instantiating the template complex for any type other than float,
> double or long double is unspecified". Thus, complex quad precision with it
> is probably a bad idea and, if I'm not mistaken, the standard does not
> state that the class must store data in the form
>
> double real, imag;
>
> so this could potentially break interfaces (e.g., to BLAS or LAPACK).
> Maybe it would be worthwhile to avoid usage of std::complex and
> simultaneously fix the compatibility issue with cusp::complex. I recently
> ripped std::complex out of Elemental for the above reasons.
>
> Jack****
>
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